Battery charger.

[Dieselman]

If one has dormant cars it's still necessary to perform some maintenance, keeping tyres blown up and in particular batteries need to be kept charged to stop degradation and freezing. A flat lead acid battery will freeze in cold conditions, whereas a charged one is much more resilient.

Every so often I connect my battery charger and have noted on two batteries last week they weren't accepting charge, even though I know the charger was able to deliver, having tested it by directly powering a battery operated electric drill.

I thought I needed two new batteries, but borrowed a battery analyser to check one.
The battery had been on charge for two days, but was only at 11.2V and apparently, iirc, 31% charged. It started the engine quickly and and the analyser said it was good and only required charging.

That made me think how a charger works...

As batteries lose charge the internal resistance reduces, so allows more current to pass from the charger. This means as batteries charge back to full capacity they naturally increase resistance and reduce the current they will accept, until accepting virtually no current when fully charged.

I investigated the charger and found the fuse holder which was mounted underneath the unit so taking impacts when standing up, was melted, presumably due to a bad contact as a result of damage.
I cut out the fuse holder and made a temporary connection, tucking the fuse inside the case, which is a bit inconvenient if it blows.

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The charger then functioned normally, but caused me to think if it could be made better, especially as the output wire insulation had also been melted by the fuse holder heat.

There's not much to a battery charger, especially not this one: I've had a smart charger before so wanted to avoid them when I bought this one.
The workings are a transformer with various output tapping's, a pair of switches to select different transformer output coils, a bridge rectifier and an ammeter.

After repairing the cabling, crimping and soldering the connections, moving the cables and fuse holder to the front from underneath, I now have a charger delivering it's full potential, instead of internal resistance causing low current output.

A pic of it still delivering a reasonable current after it had been charging a flat battery for a couple of hours.

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The label became damaged when, after gluing the fuse holder in from the rear, I went to glue the front side, realising the label needed to be removed. I already had mixed epoxy and quickly scraped the label off with a screwdriver...

[Julianw]

Nice bit of repair/improvement work there, Will!

I get by with a Ring smart charger (it's never occurred to me that it might have a fuse in it, other than in the mains plug) and it's ok. It gets a lot of use. I have had to fool that into charging a very flat battery by connecting a healthier battery in parallel - if it doesn't read a few volts from a battery, it assumes no battery is connected. And it periodically decides a battery is faulty after charging it for a while, when the battery seems quite healthy. The battery conditioning function, which has eked a little more life out of some quite sickly batteries, is its redeeming feature.

Let's not even mention the black magic going on inside modern Li-ion jump packs! I've tried a few, and think they're vastly overrated - my go to is a small traditional lead-acid powered pack, which I treated to a new battery a few years back, but otherwise it is as Maplin (!) sold it some fifteen years ago - with a compressor built in - which again has saved my bacon many times over.

(I miss Maplin)